Non-Structural High Voltage Battery

Last updated: December 11, 2024

Overview

The high voltage (HV) battery is the primary energy storage device in the vehicle. Its main purpose is to provide power to the powertrain for all vehicle operations.

The HV battery hosts several key components of the powertrain that are vital for vehicle functions like driving, charging, and providing power to the vehicle low or medium voltage (referred to as LV or MV) systems.

Warning

The HV battery has a lot of energy stored in a small volume. Use extreme care when handling HV batteries.

Location of the High Voltage Battery

The HV battery is mounted to the chassis bottom for easy removal and installation, improving vehicle dynamics with a lower center of gravity.

HV Battery Location

The HV battery is not designed for rapid HV battery swapping, nor does it have HV rapid mate connectors between the HV battery and the HV powertrain. The HV battery has latch-on HV connectors, and the coolant hose connections are clamped (not via rapid mate).

The battery pack is integral to the chassis, so removing it without first removing interior components can cause them to be pulled out with the battery.

When all the attached components are removed from structural HV battery, the HV battery looks similar to a non-structural HV battery from the outside (except for the mounts of the seat rails).

Pack Generations

Below are the different generations of Tesla HV batteries:

HV battery Generation	Applicable Models
Gen 1	2012-2020 Model S 2015-2020 Model X
Gen 2	Model 3 Model Y (Non-Structural and structural HV batteries)
Gen 3	2021+ Model S 2021+ Model X
Gen 4	Cybertruck

The Gen 2 HV battery pack debuted in 2017 on Model 3 and later on Model Y in 2020. At launch, was available in the All Wheel Drive (AWD) Long Range configuration, equipped with a 74 kWh E3 HV battery. The AWD HV batteries vary depending on charging type (three-phase or single-phase) and the presence of a front drive inverter connector.

Note

For more information, see HV Architecture Theory of Operation

In late-2021, the HV battery increased energy capacity again to 60 kWh.

Pack Architecture

The HV battery consists of the two distinct sections:

• The module platter
• The Ancillary Bay
• The rear access service panel
• The pyro-disconnect area

The HV battery module platter includes battery cells and thermal management components, and the Ancillary Bay holds electronic components known as "high voltage devices." For more details, see HV Devices Theory of Operation.

1. Rear Ancillary Bay 2. HV battery Platter
HV Battery Architecture Sections

Battery Platter

The HV platter is the large area of the battery that is below the Ancillary Bay and inside the enclosure. It contains the modules, high voltage distribution links, and thermal elements of the HV battery. The High Voltage Devices of the HV battery are located in the Ancillary Bay. The only piece of HV electronic that is not in the Ancillary Bay is the set of Battery Monitoring Boards (BMB) which are located in the modules of the HV battery.

The platter contains all the cells which have a minimum voltage of 2.5V closed circuit and a max voltage of 4.2V open circuit. With a s-count of 96, the HV battery has a minimum voltage of 240V and a maximum of 403V.

Warning

The top cover is not removeable in service. The top cover is bonded to the enclosure and all cell-arrays with adhesive. The cover cannot be removed without being damaged. Only specifically trained personnel shall remove the HV battery cover.

Note

For more information about the Ancillary Bay, refer to the Ancillary Bay Theory of Operation.

Ancillary Bay

The Ancillary Bay contains most of the HV electronics in the HV battery used to control the HV system of the vehicle. This includes:

• Powering up the HV system of the vehicle
• Charging the vehicle HV battery
• Providing power to the low- voltage system
• Managing power available for the HV system
• Managing HV system failures
• Managing thermal condition of the HV battery

The Ancillary Bay allows access to most components of the HV battery, aside from modules and the platter thermal cooling system.

Ancillary Bay Location

Ancillary Bay with Cover Removed

The Ancillary Bay contains:

HV Device	Purpose
Power Conversion System (PCS)	Converts AC to DC when charging Converts DC to DC to support thelow- voltage system Supports precharge of the HV bus before closing pack-contactors
High Voltage Controller (HVC)	Includes the High Voltage Battery Management System (HVBMS) and High Voltage Processor (HVP)
Fast Charge Contactors	Connect the HV battery to the charge port for DC charging
Pack Contactors	Connect HV from modules to vehicle powertrain
HV Shunt	Measures HV current
HV Pyro-disconnect	Disconnects HV when specific HV failure is detected (previously called a pyro-fuse)
Charge inlet connector	Connects PCS input to the charge port
HV fuses	Switched PCS HVDC input/output -63 AHeat Pump Compressor -63 A
HV connectors for the drive units and ancillary system (compressor and others)
Harnesses, busbars, coolant lines

1. Charge port connector (has changed to bolted joints in Q4 2020) 2. Fast charge contactor assembly 3. Coolant line to PCS 4. Power Conversion System (PCS)) 5. High Voltage Controller (HVC)) 6. Low voltage connector to HVC from vehicle 7. LV output from PCS 8. Positive HV battery-contactor 9. Coolant line to PCS 10. Right side Flood port 11. HV connector to cabin heater and compressor 12. Cabin heater, compressor and PCS DC output fuse (on positive DC Link) 13. HV connector to rear drive unit 14. HV shunt or current sensor 15. HV pyro-disconnect 16. HV connector to front drive unit 17. Left side Flood port 18. Negative HV battery-contactor 19. Connector for 3 phase AC charging (EU/APAC)
Ancillary Bay Components

Located under the rear passenger seats, the Ancillary Bay cover can be accessed and removed without taking out the HV battery.

The pyro-disconnect is accessible after removing the entire Ancillary Bay cover when the pyro-disconnect trips and needs replacement (usually after any airbag or pretensioner deployment).

High Voltage Interfaces

The HV battery integrates the functionality of the on-board charger, DCDC converter, High Voltage Junction Box (HVJB), and Front Junction Box (FJB) to receive and transmit signals to most powertrain electronic control units (ECUs) in the vehicle and powers on bank of the low- voltage system through the power conversion system. To achieve all this, the following interfaces exist on the HV battery:

1. Charge inlet connector 2. Three phase charge inlet connector 3. Front Drive Unit connector at HV battery (connector reference FDU-HV-AT-HVBATT) 4. Rear drive unit connector at HV battery (connector reference RDU-HV-AT-HVBATT) 5. Four pole HV connector for ancillaries (PTC heater and compressor) - (connector reference CMP-HV-AT-HVBATT) 6. Ancillaries front HV connectors (only one connector for cars with heat pump and without PTC heater) 7. Front drive unit HV connector (connector reference FDU-HV-AT-FDU) 8. Logic connector at Ancillary Bay (x098)
HV battery interfaces

Modules

Specifications

The HV battery is made of 4 independent modules, two outer modules shorter than two long central ones.

The module contains the cells of the HV battery and it is the source of energy and power for the vehicle. Each module is equipped with:

• Current collectors to connect cells together and transport current
• A Battery Monitoring Board (BMBs) connected to the current collectors to measure brick voltages and module temperatures
• Cooling tubes to cool or heat cells
• High Voltage terminals to connect to other cell-arrays or to HV devices
• Current collector fusing capability to protect from high voltage shorts

Note

For more information about BMBs, refer to the Battery Management Board Theory of Operation.

For 2170 based modules : - Short outer modules are made of 23 bricks in series which sums up to a voltage of 82V per cell array. - Long inner modules are made of 25 bricks in series which sums up to a voltage of 90V per cell array.

For LFP based modules : - Short outer modules are made of 25 bricks for LFP55 or 26 bricks for LFP60 in series summing up to a voltage of respectively 80V and 83.2V . - Long inner modules are made of 28 bricks (both for LFP55 and LFP60) in series summing up to a voltage of 90V per cell array.

Operation

Cells

Cells are the source of energy and power for the vehicle.

The HV battery has an internal structure of lithium ion cells linked together in combination of parallel and series to reach the desired level of energy and power required.

The lithium ion cells have a high energy density (Wh/kg), about 2 to 3 times the energy density of a nickel-metal hydride battery and 6 times the energy density of lead acid battery. Lithium ion cells are agnostic to charge and discharge patterns. When not in use, lithium ion cells self-discharge and have a flat discharge curve, meaning they have linear power capability even at half charge level.

Rechargeable batteries perform reversible electrochemical reactions at the battery’s positive and negative electrodes. The battery is charged by applying an electric current.

During discharge, lithium ions de-intercalate from the negative electrode and move through a separator to intercalate in the positive electrode. When charging, the reverse occurs. Lithium ions de-intercalate from the positive electrode and move through a separator to intercalate in the negative electrode.

The cells used in the HV battery have a 2170 form factor. Below is a quick reference table to what cell types are used in which HV battery.

Cell Type	Applicable Models	Production Dates	Pack Production
2170	Model 3 Model Y	Since 2017	Gigafactory Nevada Gigafactory Shanghai
Lithium Iron phosphate (LFP) Brick shape	Model 3 Model Y	Since September 2020	Gigafactory Shanghai
Lithium Iron phosphate (LFP) Blade shape	Model 3 Model Y	Since Nov 2022	Gigafactory Berlin
4680	Model Y (2020-2023 Dual Motor only)	Since October 2020	Gigafactory Austin
4680	Cybertruck	Since November 2023	Gigafactory Austin
18650	2012-2020 Model S 2012-2020 Model X	2012 to 2020	Gigafactory Fremont
18650	2021+ Model S 2021+ Model X	Since 2021	Gigafactory Fremont

1. 18650 cells 2. 2170 cells 3. 4680 cells
Comparison of Selected Cell Form Factors

A HV battery's "s-count" refers to how many cells are connected together in a series and is proportional to the HV battery voltage. A HV battery's "p-count" refers to the number of cells in parallel in a HV battery and is proportional to how much current The HV battery can deliver.

Note

The total number of cells for a HV battery is the s-count multiplied by p-count.

HV battery Generation	Configuration	Cell Type	S-Count	P-Count	Total Cells in Pack
Gen 2	Standard Range 2170	2170	96	31	2976
Gen 2	Standard Range LFP	LFP	106	1	106
Gen 2	Standard Range LFP2	LFP	102	1	102
Gen 2	Mid-Range	2170	96	37	3552
Gen 2	Long Range	2170	96	46	4416
Gen 2	Structural Standard Range	Blade	105	1	105
Gen 2	Structural Dual Motor	4680	96	10	960

Bricks in Bandoliers

A brick is a group of cells connected in parallel. Linking cells in parallel adds current from each cell to increase current capability and the amp hour count (the unit for measuring the energy capacity of a battery).

The bricks are connected in series in a module to increase voltage. The modules are also chained together in series to further increase voltage and power capability.

A bandolier refers to one or two strings of cells against a cooling tube. A module is made of 7 bandoliers.

The cells in the bandolier are positioned vertically and oriented in the same direction (one brick with anode facing up and the next brick with anode facing up).

Modules are separated by a cross member running length wise in The HV battery. There are three inner longitudinals between each module and two outer longitudinals between the outer modules and the edge of the battery. The outer longitudinal protects the modules during side vehicle impacts.

The top of the cells of each brick are spot welded to two current collectors.

• One current collector is connected to two bricks (positive of one brick and negative of the other one).
• A single collector will be connected to cells.
• Half of a collector will be connected to the can of the cells (anode) and the other half are connected to the center tab (cathode).

The current collector performs the following functions:

• Electrically interconnects cell-arrays in a series of parallel groupings,
• Distributes current between all cells in a given parallel grouping,
• Allows terminal voltage sensing, at a single point, for all cell in a given brick,
• Conducts peak and continuous operating currents between each cell and array,
• Fusing protection for HV shorts.

High Voltage Chain

Current and power accumulate along the cell-array, beginning at the first brick on the most negative end and growing to the positive end of the array, with HV terminals at each end to facilitate connection.

Note

The front terminals are designed to fuse under short circuit events at the cell-array level.

For detailed information on how the voltage builds up in the HV battery, refer to the HV Architecture Theory of Operation

Serviceability

Modules are not serviceable because they are embedded within the platter area, making them inaccessible due to the structural HV battery's bonded top and bottom enclosures.

Battery Management Board

Specifications

A BMB is a Printed Electrical Circuit Board (PCBA) with various electrical components on it. The primary functions of a battery monitoring board (BMB) are:

• Measuring voltages of the bricks in a module
• Measuring temperatures of modules in one or several locations
• Balancing bricks charge level amongst other bricks

BMBs are connected to both sides of each brick in a module.

The wires linking current collectors to BMBs are consolidated into a flexible ribbon cable called the Voltage Sense Harness (VSH).

BMBs have two thermistors mounted directly on the PCBA close to where the bandolier cooling tubes contact the BMB PCBA. The temperature of the module can be measured without requiring extra wiring between BMBs other locations on the module.

BMBs connect to each other via a daisy chain which itself is connected to the high voltage controller (HVC). Temperature and brick voltage measurements from BMBs travel on this daisy chain to the HVC. If the daisy chain is interrupted or cut anywhere, the data from BMBs can travel the other direction to the HVC.

BMBs are equipped with an analog to digital converter (ADC) to get the brick voltages and temperatures into a format that can be sent on a digital communication protocol. They also embed a multiplexer to send each measurement in sequenced order on the daisy chain.

BMBs contain one power resistor and Field Effect Transistor (FET) per brick. The FET enables a resistor to be connected in parallel with the brick, allowing for controlled energy dissipation and balancing of brick charge levels in the HV battery. BMBs only perform this passive balancing and do not charge the least charge bricks (known as active balancing).

Each cell on the picture is equivalent to a brick
Passive Balancing with Discharge of Most Charge Bricks

Operation

The BMB functions of measuring module voltage and temperature and balancing brick charge levels are critical to operating the HV battery and the vehicle. A BMB not operating as expected can prevent vehicle charging or starting, and may also cause reduced power or graceful power-off with a 30-second warning while driving to pull over before contactors open.

BMBs continuously monitor temperatures and brick voltages during charging, driving, and low-voltage system support. When the vehicle is asleep, the HVC wakes the BMBs every 10 minutes for them to report measurements and ensure brick health.

BMBs will balance the bricks when the HVC enables balancing. The HVC enables brick balancing only when the charge level of bricks has enough charge or voltage difference, and the least charged brick is above a certain threshold.

BMBs don't have embedded advanced micro processing capabilities. Their duty is to sense voltage, temperatures, and be able to put a resistor across a brick for balancing. All the processing happens in the HVC, which requires the measurements provided by the BMBs. To get the data from BMBs to the HVC, there is a daisy chain leaving the HVC, going through all BMBs in series and back into the HVC.

The daisy chain communication is bi-directional. If the daisy chain is cut anywhere, all BMBs can still communicate to the HVC.

Note

Model 3 and Y HVBMS is named HVBMS in UDS commands. This is to differentiate from Model S and Model X UDS commands nomenclature.

Serviceability

BMBs not serviceable because they are embedded within the platter area, making them inaccessible due to the structural HV battery's bonded top and bottom enclosures.

High Voltage Battery Thermal Management

Specifications

The HV battery uses liquid based thermal systems to keep battery cells at their optimized temperature and to control heat generated during conversions between AC/DC and AC/DC power. The thermal systems are split between cooling the Power Conversion System (PCS) and the cells within the cell-arrays.

Power Conversion System Thermal Loop

The PCS cooling loop consists of:

• Coolant passthrough to connect external coolant lines to the ones going to the PCS inside the HV battery.
• Inlet coolant hose bringing external coolant to the PCS.
• The PCS cooling plate on which electronic components of the PCS are mounted.
• Temperature sensors on the PCS Printed Electrical Circuit Board (PCBA).
• Outlet coolant hose to push the warm coolant back out to the external cooling system.
• Temperature sensor at the coolant inlet into the HV battery.

The PCS coolant inlet and outlets are located at the front of the HV battery directly through the ancillary bay cover.

1. Coolant outlet out of the ancillary bay 2. Coolant inlet into the ancillary bay 3. Coolant inlet into the HV battery for the ancillary bay
PCS / Ancillary Coolant Loop

Cell-Array Thermal Loop

The platter cooling system consists of:

• Coolant passthrough to connect external coolant lines to the ones to the cell-arrays.
• Inlet coolant manifolds to split the coolant flow to all the cooling tubes of the HV battery.
• Cooling tubes thermally connecting the cells to the coolant.
• Outlet manifolds to collect the coolant back from all the cooling tubes .
• Outlet coolant hose to push the coolant back out to the external cooling system.
• Temperature sensors on each BMB.

1. Module coolant outlets 2. Coolant line from ancillary bay to rear drive unit 3. Coolant inlet to Ancillary bay
Coolant Ports of the HV Battery Platter

Operation

Power Conversion System Thermal Loop

The PCS requests a desired temperature to VCFRONT. VCFRONT aggregate all the component temperature requests and appropriately set the pumps speeds and the coolant loop state.

The coolant coming from the PCS inlet passthrough will travel in the PCS cooling plate where heat will be transferred from the PCS electronics to the coolant. The coolant, from the hot electronics, will exit the PCS to get back to the vehicle cooling system where heat will be transferred to the outside air of other components that requested heat.

Cell-Array Thermal Loop

The HVC calculates the desired coolant temperature based on brick State of Charge (SOC), temperatures, and vehicle state, sending it to VCFRONT. VCFRONTaggregates this data to control pump speeds and coolant flow. The output is either hot or cool coolant traveling through the cooling tubes of the platter.

In the cell-arrays, each cell has about a third of its surface in contact with a cooling tube. The entire height of any cell contacts the cooling tube to ensure homogenous temperature along the cell.

Each module has 7 cooling tubes running length

Serviceability

The PCS cooling system is serviceable:

• The PCS can be replaced if the cooling plate has a blockage or is leaking.
• The coolant hoses from the Ancillary Bay cover to the PCS are also replaceable if damaged.
• The coolant hoses and passthroughs set up on the HV battery avoids any spillage in the Ancillary Bay upon disconnection and avoid having to drain coolant for other service actions in the Ancillary Bay that do not involve PCS.
• Service can disconnect coolant connections at the passthrough (coolant will leak outside) and plug the passthroughs. From there, the PCS and with the coolant hoses connected can be removed as one unit preventing any spillage.

The platter thermal system is not serviceable because its components are embedded within the platter area, making them inaccessible due to the structural HV battery's bonded top and bottom enclosures.

Overpressure / Overtemperature Dissipation

Specifications

The HV battery needs to be able to handle thermal runaway events internal to the HV battery in a controlled manner. Those events are sometimes caused by:

• Significant external damage to the HV battery causing cell penetration or deformation
• An internal coolant or other liquid flood. In rare cases, it can also be caused by some internal failures in the HV battery.

The HV battery features the following hardware to control runaways:

• Pack venting to allow controlled release of internal HV battery overpressure. The HV battery uses vents to allow the pressure in the enclosure to vent if pressure builds up inside the HV battery.

• Flood ports to allow automated drainage of any liquids trapped in the HV battery. Flood ports open when liquid contacts the inside of the flood port on the HV battery side (and not when liquid contacts the section of the flood port sticking outside of the HV battery).

The flood ports are two mechanical valves that open in the presence of liquid. Both ports have a cellulose ring that dissolves in contact of liquid. This causes a plastic retainer to let go a spring which opens the valve to let the liquid drain from the Ancillary Bay .

1. Left flood port 2. Right flood port
Flood Port Location

The diagram below shows the complete flood port, the arrow shows where the HV battery enclosure sits. Anything above the line is in the Ancillary Bay and below is outside the HV battery.

Flood port position per HV battery enclosure

When enough liquid is present in the Ancillary Bay , it will make its way to the flood port and reach the cellulose based ring that will disintegrate when in contact with liquid.

Cellulose based dissolving ring

Once the ring is dissolved, it frees plastic tabs from stopping the valve to come down. The pointy shape of the tabs and the spring force on the valve will cause the valve to spread the plastic tabs and the valve will move down from the spring force.

1. Plastic tabs freed without the cellulose ring 2. Spring pulling the valve down 3. Valve being pulled down 4. Opening created at the bottom of the valve to let liquid out
Cellulose based dissolving ring

The cellulose base ring is not serviceable and once the flood port is opened, it needs to be replaced. The flood port is replaceable in service from the outside of the HV battery. A small custom tool is needed to insert a new flood port.

Note

that the first couple of years of production of Model 3 HV batteries had a flood switch sensor to sense whether the flood port was opened or not. It was discontinued as not always accurate and the data flood port open or closed did not necessarily need to impact the vehicle behavior or trigger a customer visible alert.

Operation

Pack Vents

If pressure builds up inside the HV battery, the umbrella valves are designed to open outward, allowing pressure to escape the enclosure if it builds up inside. It is a one-way valve, designed so that air or other environmental debris will not enter the HV battery. The umbrella valve will disintegrate under high heat. Once disintegrated, it creates a large opening to allow faster expulsion of high-pressure gases inside the HV battery.

Flood Ports

Any long standing liquid inside the HV battery is concerning, it could overtime create soft short between cells that could generate uncontrolled heat. Flood ports automatically drain any liquid inside the HV battery to below modules. A flood port is a mechanical one way valve that opens in presence of liquid. It has a cellulose element that expands upon contact with liquid. This causes a plastic retainer to release a spring that opens the valve to let the liquid drain from the Ancillary Bay . The flood port design helps:

• Prevent hazardous pooling of fluid inside the HV battery volume.
• Seal against liquid/gas passage into the HV battery from outside.

The flood port is one time use, once it opens, it cannot close back and needs to be replaced. However, the flood ports are replaceable in service from the outside of the HV battery by twisting and pulling. It is likely that a plastic tab will break and fall into the HV battery, which is okay.

Serviceability

Both vents and flood ports are replaceable in service if damaged, missing or opened. They snap on to the enclosure from the outside of the HV battery (flood port require a twist before being pulled out)

Note

If it is suspected that a HV battery has liquid in the platter, service is responsible for draining the liquid as soon as possible.

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